1. Field of the Invention
The present invention relates to the protection of magnetoresistive ("MR") recording heads from damage caused by electrostatic discharge ("ESD"). More particularly, the invention concerns a method and apparatus for providing ESD protection by shorting MR heads during selected times.
2. Description of the Related Art
Many modern disk drives employ MR recording heads, also called "MR heads", "MR sensors", or "MR elements". MR heads provide improved performance in a number of important respects. However, compared to previous generation thin-film recording heads, MR heads are typically about 100 times more sensitive to damage caused by ESD. Some tests have estimated 14,000 volts as the failure voltage for one model of IBM's thin-film inductive recording head. This estimation was made using the known Human Body Model of failure analysis, known as "HBM". In contrast, tests of conventional MR heads indicate an HBM failure voltage of only 150 volts. These tests simply reflect one known characteristic of MR heads their high susceptibility to damage from ESD.
During operation of a magnetic storage drive, ESD is typically a relatively insignificant problem. The storage drive is usually encased within a computer, where it is protected from static discharge, particle contaminants, human interference, and other damage. In contrast, during the manufacture of magnetic storage drives, ESD can be a significant and perplexing problem, significantly reducing the effective yield of manufacturing operations.
As a result, engineers are continually seeking effective ways to prevent ESD damage during manufacturing operations. Traditionally, one of the best ways to reduce yield losses from ESD damage is to short the leads of an MR head together. This provides an electrical discharge path around the MR element, rather than through it. Experiments conducted by the inventors using a conventional MR head have shown that spanning the MR sensor with a 1 ohm connection increases the HBM failure voltage from 150 to 2000 volts.
Although the MR sensor is protected from ESD when its leads are shorted, this effectively renders the MR sensor inoperative. Therefore, to activate the MR sensor for manufacturing tests and the like, the shorted leads must be removed, disabled, or otherwise electrically disconnected. Likewise, after such tests, the interconnection between the leads must be reconnected to protect the MR sensor again. Manually shorting the leads in this manner, however, fails to provide a sufficiently convenient mechanism for protecting the MR head.